...dog drops a lit tle black plas tic bag in to a rub bish bin. In sid e the bag is dog poo. Sam: It might make it seem that hu mans are hy gi enic cre at ures - cer tainly clea ner than dogs, who go to the toil et wher e ver they want. But is this the whole sto ry? Neil: How do us hu mans com par e...